JERUSALEM, FEB. 12 -- Internal Israeli divisions over the new U.S. Middle East peace initiative increased sharply today with Prime Minister Yitzhak Shamir bitterly accusing his chief political rival, Foreign Minister Shimon Peres, of being prepared to "sell everything we have" to the Americans on the peace issue.

Meanwhile, soldiers shot dead two more Arab youths in the West Bank city of Nablus. At least 54 Palestinians have died during the two-month-long wave of unrest in the occupied West Bank and Gaza Strip.

The two Palestinians killed today were boys aged 17 and 14, according to Israeli radio, which said they were shot during fierce clashes in narrow alleyways of Nablus' central market after Friday prayers at a mosque.

Rioters threw stones, firebombs, building blocks and flowerpots at Israeli troops, who fired back with tear gas and rubber bullets and eventually with live ammunition when the violence "got out of hand," the radio reported. Five Palestinians were injured.

{The Associated Press reported from Nablus that soldiers broke windows to enter the city's Ittihad Hospital, where they beat and detained four Palestinians who were giving blood. The Army said it was investigating the incident.}

Shamir, in his first public comments since U.S. envoy Richard W. Murphy unveiled to the Israelis a new set of American ideas aimed at producing direct Arab-Israeli peace talks, launched an unusually angry and caustic assault on Peres, with whom he has shared the leadership of Israel's fractious national unity government for the past four years. Shamir accused Peres, leader of the more dovish Labor half of the coalition, of being prepared to "surrender" on vital points prior to negotiations.

Shamir also accused the Labor leader of duplicity and of leaking confidential materials to the press. Peres "thoroughly conceals every step he takes, operating in the dead of night," said Shamir, leader of the more hawkish Likud.

"He wants to know what I am doing in order to make it fail," said Shamir in an interview with Israeli radio. "How can you conduct negotiations together when your partner runs to the other negotiating party, the other side, every day, every moment, and says: 'I'm selling for less. Don't listen to what Shamir says'?"

The prime minister also took a swipe at U.S. diplomats. After Israel made what Shamir said was a huge concession in the 1978 Camp David accords, "Now they come and tell us: 'Forget about it -- that concession has already been made. Now we want new concessions.' "

Shamir's remarks followed comments by Peres yesterday in which the foreign minister suggested that the wave of Palestinian unrest could have been avoided had Shamir acceded to Jordanian King Hussein's demand for an international Middle East peace conference last year.

Peres had asked a Labor Party central committee meeting a series of questions that blamed the Likud and its support for Jewish settlements in the occupied territories for scuttling the peace process:

"Let each of us ask himself: Do the settlements, this dandy enterprise, provide security? Have they strengthened our position in the negotiations? Let each of us ask himself: If we did not have to keep so many troops in Gaza, could we not bring about quiet in the place that is most essential to us today, Jerusalem?"

Aides said Shamir has been deeply angered by Israeli and foreign press reports indicating he had rejected Murphy's proposals this week. They said Shamir, despite deep reservations, is in fact seeking to remain flexible and blames Peres for press leaks characterizing Shamir's position as a rejection.

Murphy presented what officials here described as "ideas" rather than a definitive plan for restarting the dormant peace process. They include some sort of international event in April as a forum for beginning direct talks between Israel and a joint Jordanian-Palestinian delegation, an interim agreement that would grant limited autonomy to Palestinians in the occupied territories and the opening of talks on a final settlement in the territories by year's end.

Peres has endorsed the proposals as the only realistic possibility for a breakthrough. Shamir has not spelled out publicly his differences with the American ideas, but advisers say he still opposes the idea of an international conference and does not like Murphy's proposal that a rigid timetable be set for beginning talks on a final settlement.

Peres and Shamir face general elections in November and their responses to the U.S. initiative are likely to include calculations about their political impact. Peres, in embracing the new proposals, hopes to enhance his image as a peace advocate, while Shamir wants to appear firm but not intransigent.

"If we want to conduct negotiations, we must examine every condition, every clause to see if it suits our interests entirely, and argue and haggle," Shamir said in his Israel radio interview. "Otherwise peace cannot be achieved."